The present invention relates to apparatus for treatment of a fluid wherein a semipermeable membrane is utilized to separate a permeate from waste fluid, and more particularly to a membrane tube through which a volume displacement rod extends and to the structure for supporting the rod in the fluid flow stream so as to avoid obstruction of the flow of fluid and to assure optimum performance of the membrane.
Membrane separation processes employing tubular membranes are well-known in the prior art. United States Pat. No. 3,834,545, patented Sept. 10, 1974 in the names of Del Pico et al., discloses a membrane tube that is suitable for use in a separation process. Membrane tubes of this character can be used in a variety of different separation processes, including the process which is disclosed in United States Pat. No. 3,950,249, patented Apr. 13, 1976 in the names of Eger et al. The process disclosed in this patent involves recovery of water from the effluent discharged by a biological treatment system, the water then being available for reuse in the flushing system that discharges to the biological treatment system.
It has been found beneficial to insert a volume displacement rod axially through the membrane tube, as is shown in FIG. 14 of U.S. Pat. No. 3,950,249, to improve the efficiency of operation of the membrane tube and to aid in maintaining the inner surface of the semipermeable membrane in a clean state. This has been done by constructing spider-like support structures that can be secured at the ends of the membrane tube, and the rod is supported at its ends by these spider-like structures. This construction and arrangement is not entirely satisfactory in use. This spider-like structures interfere to some extent with the flow of the fluid, and this defect becomes increasingly more pronounced as the spider-like structures accumulate or become coated with solid waste particles. Also, the rod is held firmly between the support structures, and due to thermal expansion and flow characteristics of the fluid, the rod, which has generally been constructed of a flexible material, may bow out of alignment with the axis of the membrane tube. This then causes non-uniform flow of the fluid through the annular passageway defined between the rod and the semipermeable membrane resulting in certain areas of the membrane being less productive than other areas.